Over the past seven years in the Cleveland, Ohio area there have been 47 cases of unexplained pulmonary hemorrhage in young infants. Sixteen of the infants have died. A CDC case-control study found an association with water-damaged homes and the toxigenic fungus, Stachybotrys chartarum, which requires water soaked cellulose to grow. The spores of this fungus are not infectious in the lung but do contain very potent mycotoxins which appear to be particularly toxic to the rapidly developing lungs of young infants. Secondary stresses, e.g. environmental tobacco smoke, appear to be important triggers of overt hemorrhage. Concern that there may be a larger number of undetected young infants with this disorder led to the examination of all infant coroner cases, which revealed six sudden infant death syndrome cases with major amounts of pulmonary hemosiderin-laden macrophages, indicating extensive hemosiderosis existing prior to death. All of these infants had lived in the eight zip code area where all but fifteen of the patients have lived. This disorder may extend beyond Cleveland since toxigenic fungi are widespread. We are aware of a total of 138 infants with idiopathic pulmonary hemorrhage across the country over the past four years.